Effects of moxidectin on coprophagous insects in cattle dung pats in Japan

Effects of the antiparasitic drug moxidectin were studied in laboratory and field experiments in Hokkaido, Japan by pour-on administrations (500 µg/kg) on a target pest Haematobia irritans Linnaeus, nontarget coprophagous flies represented by Neomyia cornicina (Fabricius), and the dung beetle Caccobius jessoensis Harold. The concentration of moxidectin excreted into cattle dung was maximum at 3 days post-treatment both in the first and second trials, and then it diminished. No moxidectin was detected on or after day 21 post-treatment in the first trial, and on or after day 28 post-treatment in the second trial. Larval development of H. irritans was hampered from 1 to 7 days post-treatment. No N. cornicina pupated in dung at days 1 and 3 post-treatment, and pupation and emergence rates were reduced in the dung until 7 days post-treatment. There were no significant differences in numbers and weight of brood balls constructed by Caccobius jessoensis in dung from treated and control cattle. Adult emergence rates of C. jessoensis on days 1, 3, 7, 14 post-treatments were not significantly different between control and treated groups, and more than 90% of adult emergence rates were demonstrated in both groups. In the field study using emergence traps, 3,433 (18 families) flies emerged from dung from untreated control cattle and 1,667 (16 families) flies emerged from dung from treated cattle. Notably, the number of Sciaridae spp. (first Experiment) and Sepsis latiforceps Duda and Sphaeroceridae spp. (second Experiment) significantly decreased in dung pats of treated cattle. From 48 dung pats in the field experiments, total dry weight of major coprophagous flies that emerged was 1,741.8 mg in dung from control cattle and 1,170.0 mg in dung from treated cattle, showing 32.8% reduction in treated dung. Emergence rates of C. jessoensis from brood balls recovered from soil beneath dung pats in the field experiments were not significantly different between dung from control and treated cattle on each sampling day (1, 7, 14, and 21 days) post-treatment.